The invention relates to curable effect providing coating systems and more particularly to two layer effect providing coating systems.
Coatings have long been used to provide a protective finish for vulnerable or exposed substrates. Such systems typically provide protection from the effects of outdoor exposure and use as well as resistance to corrosion and chemicals such as acids, solvents and the like. However, the atheistic visual appearance or effect provided by a coating composition or system is equally important, particularly in the automotive industry.
Although automotive basecoats and topcoats were once primarily relied upon to provide a single color effect, more recent years have seen the introduction of metallic, pearlescent and opalescent color effects. Metallic effects, in which the appearance of sparkle is imparted to a finished film, are achieved by the introduction of finely divided metallic flake or mica particles into one or more layers of the coating system. Typical systems of this type are disclosed in U.S. Pat. Nos. 4,048,136; 4,499,143; and 4,605,687. Pearlescent or opalescent color effects have been achieved by the introduction of particles of mica which have previously been encapsulated in a thin layer of a metal oxide into one or more layers of the coating system. Typical systems of this type are disclosed in U.S. Pat. Nos. 4,530,258; 4,457,410; 4,551,491; 4,598,015; 4,498,020; and 4,615,940.
While many of these systems provide unique and desirable color and special appearance effects, improvements in visual appearance are constantly being sought. Improvements and new effects that are ever more lustrous, satiny or liquid in appearance are desired, especially with improved depth and clarity as well as special color highlights, hues and shifts. The most desirable appearance effects are those which make traditional colors such as white, beige, gray and the like, more interesting and appealing to the consumer.
Thus, more dramatic hue shifts, particularly in the angle of viewing available to the casual observer, i.e., a 25xc2x0 angle to 75xc2x0 angle of viewing, are especially desired. For example, an observer of a coated surface would initially percieve a first color or effect when said coated surface is viewed at a 0xc2x0 angle, i.e., perpendicular to the observers"" eye or directly opposite the observer""s line of sight. However, when the coated surface is slowly moved so as to be oblique to the observer""s line of sight, i.e., at a 25xc2x0 to 75xc2x0 angle of viewing, the observer would like to see a dramatic hue or color shift relative that first perceived color or effect. Thus, what is desired is a particular color effect which is dependent upon the angle of viewing. Such particularly desired hue shifts can provide highlight colors of red, blue, green, gold, violet, or orange to a coating system, resulting in a more aesthetically appealing appearance and effect.
While the use of metal oxide coated micas is known in coatings, i.e., see U.S. Pat. Nos. 3,087,829, 4,456,486, 4,551,491, 4,598,015, and 5,741,355, such compositions have failed to provide dramatic color shifts at the various angles of viewing. This is especially true in regards to unique appearance effects in white and/or pastel automotive body colors.
Moreover, the prior art has failed to date to provide such visual effect improvements in commercially feasible effect providing coating systems. Those prior art special effect coating systems which do provide prior art visual appearance effects generally require multilayer applications. The prior art has utilized such multilayer systems in order to balance appearance considerations with durability and protection requirements.
For example, U.S. Pat. Nos. 4,539,258 and 4,615,940 describe a multilayer coating system wherein a least three coating layers must be used to provide the desired opalescent effects. In such systems, the opalescent effect derives from the use of a primer layer or intermediate layer containing metal oxide encapsulated mica particles in addition to a basecoat and a clearcoat. The desired visual effects are obtained only with the use of the disclosed third layer. Failure to use the required third layer in conjunction with both a basecoat and a transparent topcoat results in a nondesireable visual appearance.
BASF Corporation of Southfield, Mich. provides a commerically available ivory three-layer coating system wherein a transparent topcoat is applied over an intermediate layer comprising metal oxide encapsulated micas. The intermediate layer is applied over a pigmented basecoat which has been tinted to match the xe2x80x9cflopxe2x80x9d or hue shift of the intermediate layer.
However, the application of a third effect providing coating layer is greatly disfavored in view of practical manufacturing considerations. The application of a three-layer effect providing coating system requires more space, equipment, time, and/or expense than that required to apply a two-layer effect providing coating system. It may also result in the discharge of greater amounts of volatile organic solvents as a result of the additional application step. Thus, most automotive manufacturers require the use of no more than a two-layer effect providing coating system. That is, the desired appearance must be provided by either a single topcoat or a two-coat composite system, the latter highly favored and most often being a pigmented basecoat followed by a transparent clearcoat.
Finally, many of the prior art effect providing coating systems suffer from mottling, a visual defect which detracts from the appearance of the finished film. Mottling may generally be described as an undesirable variation in the visual appearance and color at a particular angle of viewing. Mottling is believed to be a function of the varied orientation of flaked pigments in a coating, usually a basecoat, and can occur as a result of various application problems, or as a result of an inherently weak basecoat rheology system.
Mottling can sometimes be fixed by improving basecoat application or rheology. In other systems, the only possibility is to change the flake or pigment system of the basecoat or surrounding coatings, especially transparent or semi-transparent flake containing coatings. It would be advantageous to provide an effect providing coating system which provides a pearlescent or luminescent appearance and which is less likely to exhibit mottling relative to prior art effect providing coating systems.
Thus, it is an object of the instant invention to provide a two-layer coating system which provides a visual appearance and effect previously obtainable only with the use of a three layer effect providing coating system.
It is another object of the instant invention to provide a two-layer coating system which provides improvements in visual appearance and effect relative to that previously obtainable with prior art three-layer effect providing coating systems.
It is a particular object of the invention to provide a two-layer coating system that provides dramatic improvements in hue shift at viewing angles of from 25xc2x0 to 75xc2x0 degrees.
Another desired object of the invention is provide such dramatic hue shifts in conjunction with traditional colors such as white, beige, gray and the like so as to provide heretofore unknown visual effects in a two-layer coating system.
These and other objects have been achieved with the instant invention. It has unexpectedly been found that the use of certain metal oxide encapsulated mica pigments in a particular two-layer coating system results in new and improved visual effects while maintaining the performance requirements and characteristics of a commercially acceptable three-layer effect providing coating system.
The curable effect providing coating system of the invention consists essentially of a first layer consisting of a first coating composition (a), and a transparent second layer applied directly to the first layer and consisting of a second coating composition (b) comprising an effective amount of an interference metal oxide coated mica having a hue shift xcex94h of at least 100xc2x0.
In a preferred embodiment of the invention the first coating composition (a) will be tinted so as to provide a colored appearance which is matched to the color observed in the transparent second layer (b) when it is viewed at an angle of 110xc2x0 from vertical.
Most preferably, first coating composition will comprise (i) at least 95 weight percent titanium dioxide pigment and (ii) no more than 5 weight percent of one or more tint pigments selected from the group consisting of opaque yellow oxide, opaque red oxide, black, bismuth vanadate, isoindolines, quinacridones, indanthrones, phthalo, nickel azos, and benzimidazolone and mixtures thereof, all based on the total weight of the first coating composition (a).
The instant invention relates to effect providing coating systems. As used herein, xe2x80x9ceffect providingxe2x80x9d refers to one or more coating composition layers which are primarily responsible for the color of the coated surface. As such, traditional primers and/or sealers which are pigmented to achieve particular performance parameters such as corrosion, adhesion and/or smoothness, are generally not considered to be part of an xe2x80x9ceffect providingxe2x80x9d coating system. If however, such primers and/or sealers are pigmented so as to achieve an effect or color which is a part of the overall final color or appearance, said primers and/or sealers are be considered to be part of the xe2x80x9ceffect providingxe2x80x9d coating system.
The two layer effect providing coating system of the invention comprises a pigmented first layer consisting of a first coating composition (a), and a transparent second layer applied directly to the first layer and consisting of a second coating composition (b) comprising an effective amount of an interference metal oxide coated mica having a hue shift xcex94h of at least 100xc2x0, at viewing angles of from 15xc2x0 to 75xc2x0.
The transparent second layer results from the application of a second coating composition (b). Second coating composition (b) is most preferably a transparent clearcoat coating composition comprising an interference metal oxide coated mica having a minimum hue shift (xcex94h) of at least 100xc2x0, at viewing angles of from 15xc2x0 to 75xc2x0. Transparent as used herein refers to a cured or curable coating composition which permits the passage of rays of the visible spectrum.
As used herein, xe2x80x9cinterference metal oxide coated micaxe2x80x9d refers to a particular class of metal oxide coated micas, which produce a specific visual effect at a particular angle of viewing. In general, an interference metal oxide coated mica is a mica particle having a particular aspect ratio which is coated with a particular thickness of a metal oxide such that it generates a chromatic, reflective color at the flash, and an opaque complement in the face and flop.
As used herein, xe2x80x9cfacexe2x80x9d xe2x80x9cflashxe2x80x9d and xe2x80x9cflopxe2x80x9d refer to the appearance of a coated panel at a particular angle of viewing as well as the noted angle of viewing. xe2x80x9cFacexe2x80x9d is the color and effect of a coated panel when it is viewed at a 0xc2x0 angle, i.e., perpendicular to and facing the observer""s eye. xe2x80x9cFlashxe2x80x9d is the perceived color and effect of the coated panel when the coated panel is held and viewed at an angle of from 25xc2x0 to 30xc2x0 from perpendicular to the eye. Flash is generally the brightest appearance and angle. xe2x80x9cFlopxe2x80x9d refers to the color and effect perceived when the coated panel is held at an angle of from 110xc2x0 to 120xc2x0 from perpendicular to the eye.
Generally, an observer of a surface coated with a coating composition containing a masstone concentration of an interference metal oxide coated mica will perceive the xe2x80x9ccolorxe2x80x9d of the coated surface as a chalky pinkish pastel at viewing angles of from 0xc2x0 to 25xc2x0. However, when viewed from flash to flop, the same coated surface will appear to be a different xe2x80x9ccolorxe2x80x9d.
For example, a masstone coated panel can be prepared by preparing a curable coating composition having a maximum pigment to binder ratio (P/B) wherein the pigment is solely an intererence metal oxide coated mica pigment. This masstone coating composition is then sprayed to hiding, i.e., the coating composition is applied at a film build sufficient to completely obscure a black and white figure affixed to the substrate to be coated. The color differences dependent upon the angle of viewing can then be identified and quantified by spectrophotometer measurement.
This color shift from flop to flash can be described in terms of L*a*b readings and more specifically in terms of xcex94*a and xcex94*b values which reflect hue shift. Referring to FIG. 1, there is shown a simplified section through the CIE 1976 (L*, a*, b*) color space diagram based on the color measurement system introduced by Richard S. Hunter, xe2x80x9cPhotoelectric Tristimulus Colorimetry with Three Filters,xe2x80x9d National Bureau of Standards Circular 429, United States Government. Printing Office, 1942, reprinted in J. Opt. Soc. Am., 32, 509-538 (1942) which is incorporated herein by reference. A particular color can be completely described by defining its value (lightness), hue (color), and chroma (degree of color saturation). In this system the value of a color, L*, corresponds to its lightness and ranges from zero (black) to one hundred (white). The hue of a color is designated by values of a* and b*, with a* corresponding to redness (if a* is positive) or greenness (if a* is negative), and yellowness (if b* is positive) or blueness (if b* is negative). The chroma of the color is designated C* and is equal to the square root of the sum of the squares of a* and b*. xcex94*a and xcex94*b respectively refer to the color shift between particular viewing angles. Vales of xcex94*a and xcex94*b may be measured via a sphectrophotometer.